JP2007268142A - Method for measuring impedance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for measuring impedance which can compute a good accuracy value by removing the affection by the respiration of a measured person and the instability of contact resistance in the determination of the definite value of a measuring impedance value. <P>SOLUTION: In the method for measuring the impedance by an electrode 1 which is mounted on the human body, the impedance is calculated from an impedance transition accompanying the expansion and contraction of the human body by the respiration. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for measuring the impedance of an object to be measured by a four-terminal method.

  Conventionally, for example, Patent Document 1 discloses a technique using bioimpedance (BI) measurement as a means for safely and easily measuring human body fat (subcutaneous fat and visceral fat).

  The body fat measurement device using the bioimpedance measurement disclosed in Patent Document 1 has a plurality of electrodes 1 (1a, 1b) arranged on the outer periphery of the abdomen W of a human body as shown in FIG. A current is caused to flow between the two electrodes 1a (current application electrode 1a) by the constant current generation circuit 2, and the voltage generated between the other two electrodes 1b (voltage measurement electrode 1b) is measured by the voltage measurement circuit 3, Impedance is calculated from the measured voltage, and fat mass is calculated. Here, in order to remove the influence of the contact resistance due to the contact between the electrode 1 and the skin, the measurement is usually performed by the four-terminal method.

  However, when impedance measurement is performed at the abdomen W of the human body as in the prior art described above, the measured impedance value changes due to expansion and contraction of the abdomen W due to breathing of the measurement subject.

  That is, when the subject is breathing, a difference between the minimum and maximum measured impedance values of several tens of milliohms to several hundred milliohms is generated. FIG. 8 is a graph showing changes in measured impedance values during breathing. The impedance value increases when the abdomen W is inflated, and the impedance value decreases when the abdomen contracts.

  In order to eliminate the influence of such breathing, a method is usually used in which the person to be measured stops breathing when measuring impedance. However, when the impedance measurement is not stable due to the contact resistance between the electrode and the skin, there arises a problem that the subject is forced to stop breathing for several tens of seconds. An example of the time change of impedance measured in the respiratory stop state is shown in FIG. As time passes, the contact resistance between the electrode and the skin decreases due to skin perspiration and the like, and the impedance also converges to a constant value. During this time, fluctuations of several millimeters to several tens of milliohms occur. In order to obtain a deterministic value of impedance, it is feared that having the subject continue to stop breathing until the measurement value converges will not only be a heavy physical burden but also cause measurement instability. The

As described above, in the determination of the deterministic value of the measurement impedance value, there has been a problem in that a value with high accuracy cannot be calculated conventionally due to the influence of the measurement subject's breathing and the instability of contact resistance.
JP 2001-178697 A

  The present invention has been invented in view of the above-described conventional problems, and in determining a deterministic value of a measured impedance value, an accurate value can be obtained by removing the influence of the subject's breathing and instability of contact resistance. It is an object of the present invention to provide an impedance measurement method capable of calculating

  In order to solve the above problems, an impedance measuring method according to the present invention is a method in which an electrode 1 is attached to a human body and the impedance is measured by the electrode 1, and impedance is obtained from an impedance change accompanying expansion and contraction of the human body due to respiration. It is characterized by calculating.

  By adopting such a method, the impedance can be accurately calculated except for the influence of the breathing of the measurement subject and the instability of the contact resistance.

  Moreover, it is preferable that the calculation of the impedance is an average value of the maximum value and the minimum value of the impedance within a predetermined time including at least a predetermined number of breaths. In addition, it is preferable that the calculation of the impedance is an average of impedance fluctuations within a predetermined time including at least a predetermined number of breaths. Thereby, the impedance can be accurately calculated.

  Furthermore, it is preferable to determine that convergence has occurred when the impedance change within the predetermined time is within a predetermined value, and to use the value obtained by the calculation as a definite value of impedance.

  By adopting such a method, the convergence determination can be easily and reliably performed.

  Also, when the impedance does not converge, it is preferable to determine convergence again by adding the next new impedance value except the oldest impedance value.

  By adopting such a method, the measurement time can be shortened.

  In addition, the electrode 1 is attached to the human body, and the impedance is measured by the electrode 1, and when the impedance change is within a predetermined value by measuring the impedance change accompanying the expansion and contraction of the human body due to breathing, the person to be measured The timing of starting the breathing stop may be notified by the notifying means 5, and then the impedance may be calculated from the impedance change when the human body stops breathing.

  By adopting such a method, the impedance can be calculated from the change in impedance at the time of breathing stop, and the impedance can be calculated accurately, excluding the influence of the subject's breathing and instability of contact resistance, and the breathing stop Since the timing to start the operation is notified, the time during which breathing is stopped can be shortened, and the burden on the subject can be reduced.

  The present invention eliminates the influence of the expansion and contraction of the human body due to respiration on the measurement, and can accurately measure the impedance without individual differences.

  Hereinafter, the present invention will be described based on embodiments shown in the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of an embodiment of an impedance measuring apparatus used in the method of the present invention.

  The impedance measuring device applies a constant current between a plurality of sets of electrodes 1 (two current application electrodes 1a and two voltage measurement electrodes 1b) and a current application electrode 1a. A constant current generating circuit 2 for flowing, a voltage measuring circuit 3 for measuring a voltage generated between the voltage measuring electrodes 1b, and an impedance calculating circuit for calculating an impedance from the measured voltage measured by the voltage measuring circuit 3 4 and a notification means 5.

  As an example of measuring the impedance of the object to be measured using the impedance measuring apparatus, an example of measuring the impedance of the human body torso W is shown below.

  The pair of current application electrodes 1a and the pair of voltage measurement electrodes 1b are arranged on the outer periphery of the torso W of the measurement subject as shown in FIG. When a constant current is passed through the application electrode 1a, a current flows through the body W. The voltage generated between the voltage measuring electrodes 1b as a result of the current flowing through the body W in this way is obtained by the voltage measuring circuit 3, and the voltage thus obtained and the current flowing between the current applying electrodes 1a, In this case, the impedance calculation circuit 4 calculates the impedance between the voltage measuring electrodes 1b based on the constant current.

  FIG. 2 shows a flowchart for calculating the impedance by the impedance calculation circuit 4.

  As shown in FIG. 2, after the measurement is started, the first several times of acquired data are discarded in consideration of the influence of the contact resistance between the electrodes (current application electrode 1 a and voltage measurement electrode 1 b) and the skin. After the acquisition data has been truncated a predetermined number of times as described above, measurement data acquisition is started. An error is determined every time measurement data is acquired, and when the acquired data satisfies a predetermined error condition, the measurement is stopped and the process proceeds to error processing. As an example of error determination, there is a case where a numerical range that can be taken by measurement data is determined in advance and the measurement data exceeds the upper limit value of the numerical range or the measurement data falls below the lower limit value. Considering the influence of spike noise, it is preferable to determine that an error occurs when the same error appears twice in succession. These assume a situation where the electrode 1 is not properly attached to the skin. In the error determination, when the acquired data does not satisfy the error condition, data convergence determination is performed. Data acquisition is performed a predetermined number of times intermittently within a certain time period during which the measurement subject performs at least a predetermined number of breaths. Although it does not specifically limit as a predetermined | prescribed respiratory frequency, For example, 1-15 times can be selected. Convergence determination is performed for each data acquisition, and if the data is within the range of convergence determination, data acquisition is continued a predetermined number of times. Start acquiring a predetermined number of data from the beginning. The number of times (predetermined number) of data acquisition can be appropriately determined according to the material and size of the electrode to be used or the skin condition of the measurement subject. Although it does not specifically limit as a predetermined frequency, For example, 4 times-100 times are illustrated. The data acquisition is preferably performed a plurality of times within one breathing time of the subject. It is determined that the measured impedance value has converged when all the data is within the convergence determination range within the predetermined number of times. As an example of convergence determination, it can be set when the difference between the maximum value and the minimum value of the acquired data is within a predetermined numerical range. At this time, the maximum value and the minimum value may be the second value from the top and the second value from the bottom, respectively, in consideration of spike noise.

  When the impedance change does not converge, the data may be re-acquired from the beginning as described above. However, in order to shorten the measurement time, as shown in FIG. After acquisition, convergence determination may be performed again.

  In the time-out determination, if it is not determined that the time has converged within a predetermined time, the process proceeds to error processing.

  After the data acquisition is completed, an average of the maximum value and the minimum value of the predetermined number of data is obtained by impedance calculation to obtain a definite value of impedance. In order to remove the influence of spike noise, the second largest (smaller) data value may be determined as the maximum value (minimum value).

  In the impedance calculation, as shown in FIG. 4, the average of the fluctuations of the impedance may be obtained by taking the average of the entire predetermined number of data obtained as shown in FIG.

  Note that the fixed value of the impedance calculated and fixed by the impedance calculation circuit 4 as described above may be notified by the notification means 5, for example. As the notification means 5, display means for notification by characters or figures, light emission display means for notification by light, voice notification means for notification by voice, or the like can be adopted. Alternatively, the body fat mass may be calculated based on the impedance calculated as described above, and the calculated body fat mass may be notified by the notification means 5.

  Next, still another embodiment of the present invention will be described with reference to FIGS. In this embodiment, first, a convergence check process is performed as shown in the flowchart of FIG. 5 to notify the measurement subject that the data has converged, and then, as shown in the flowcharts of FIGS. Thus, this embodiment is effective when measurement is performed in a state where the person to be measured stops breathing.

  That is, it is difficult to maintain the state in which the measurement subject has stopped breathing for a long time, and therefore it is necessary to start breathing at the timing when the data has converged. For this reason, in this embodiment, in order to know the timing when this breathing starts to be stopped, the notifying means 5 is used to notify the measurer of the convergence of the data by means of characters, figures, light, or voice. It has become. By doing in this way, the time when the person to be measured stops breathing can be shortened.

  In the processing flow, first, convergence confirmation processing is started as in the flowchart of FIG. The flow of the convergence confirmation process is the same from “predetermined number of times data” to “end of predetermined number of times” from “predetermined number of times data” to “end of predetermined number of times” in the process of FIG. After the “predetermined number of times”, the convergence check is completed, and the notification means 5 notifies the measurement subject that the data has converged, that is, the timing at which the measurement subject starts to stop breathing. The fixed value of the impedance is obtained by the same processing flow as the flowchart of FIG. However, at this time, the number of times of data acquisition (predetermined number of times) and the condition for determining the convergence are set to values suitable for measurement in the breathing stop state. In general, the predetermined number of data acquisitions in the breathing stop state can be made smaller than that in FIGS. Further, the conditions for determining convergence can be made stricter than those shown in FIGS. 2 and 4 (allowable width of impedance change is narrowed). As shown in FIG. 6, the person to be measured starts to stop breathing at the same time as the notification of the convergence confirmation is made by the notifying means 5, and performs the process of obtaining the fixed value of the impedance after starting to stop breathing in this way. is there. By doing so, it is possible to perform measurement with a stable contact resistance when acquiring an impedance value in a state where breathing is stopped.

  Although the apparatus shown in FIG. 1 was illustrated as one embodiment of the impedance measuring apparatus used in the method of the present invention, the arrangement of the current applying electrode 1a and the voltage measuring electrode 1b arranged on the outer periphery of the torso W of the human body is the same. It is not limited and various arrangements can be taken. For example, the method of the present invention can be used for an impedance measuring apparatus in which the electrode 1 is arranged at a position as shown in FIGS.

  As described above, for example, body fat mass can be calculated based on the calculation result of human impedance, but it can be used as basic data for measuring various human body information in addition to the calculation of body fat mass It is.

It is a schematic block diagram of the impedance measuring apparatus used for this invention. It is a flowchart which calculates an impedance with the impedance calculation circuit of one Embodiment same as the above. It is explanatory drawing which shows an example which acquires data same as the above and performs convergence determination. It is a flowchart which calculates an impedance in the impedance calculation circuit of other embodiment same as the above. It is a flowchart which calculates an impedance with the impedance calculation circuit of further another embodiment same as the above. It is a graph which shows notifying the convergence of the impedance change accompanying expansion and contraction of the human body by respiration same as the above, and calculating an impedance from the impedance change at the time of a human body's breathing stop next. It is a schematic block diagram of the impedance measuring apparatus of a prior art example. It is a graph for explanatory drawing which shows the change of the impedance measured value at the time of respiration. It is a graph for explanatory drawing which shows the change of the impedance measured value at the time of a breathing stop. It is explanatory drawing of other embodiment which shows the example of arrangement | positioning of the electrode of the impedance measuring apparatus used for this invention. It is explanatory drawing of other embodiment which shows the example of arrangement | positioning of the electrode of the impedance measuring apparatus used for this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrode 1a Current application electrode 1b Voltage measurement electrode 2 Constant current generation circuit 3 Voltage measurement circuit 4 Impedance calculation circuit 5 Notification means

Claims (6)

  An impedance measuring method, comprising: mounting an electrode on a human body, and measuring impedance using the electrode, wherein the impedance is calculated from an impedance change accompanying expansion and contraction of the human body due to respiration.   2. The impedance measuring method according to claim 1, wherein the calculation of the impedance is an average value of a maximum value and a minimum value of impedance within a predetermined time including at least a predetermined number of breaths.   2. The impedance measuring method according to claim 1, wherein the calculation of the impedance is an average of fluctuations in impedance within a predetermined time including at least a predetermined number of breaths.   4. The method according to claim 2, wherein the impedance is determined to be converged when the impedance change within the predetermined time is within a predetermined value, and the value obtained by the calculation is set as a definite value of the impedance. 5. Impedance measurement method.   5. The impedance measuring method according to claim 4, wherein when the impedance does not converge, the convergence is judged again by adding the next new impedance value except for the oldest impedance value. A method of measuring the impedance by attaching an electrode to the human body and measuring the impedance with the electrode, and measuring the impedance change accompanying the expansion and contraction of the human body due to breathing, and starting the respiratory stop of the subject when the impedance change is within a predetermined value An impedance measuring method comprising: notifying the timing of the above by an informing means, and subsequently calculating the impedance from the impedance change when the human body stops breathing.

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